Field of the Invention
The present invention is related to an autofocus device and a sample observation device provided with an autofocus device.
Description of the Related Art
As an autofocus technique utilized in the field of microscopy, an autofocus technique of an active type as described in for example Japanese Laid-open Patent Publication No. 2006-293222 is known. According to this type, a photodetector having a plurality of light receiving elements detects light to be used for autofocusing (referred to as AF light hereinafter) that has been cast on a sample through one of the two regions obtained by dividing the pupil plane of an objective into two, and the focusing state is detected on the basis of the detected signal.
The autofocus technique based on the above type is employed by microscopes regardless of whether they are industrial microscopes or biological microscopes. However, because planes that are targets of autofocus in biological microscopes have a reflectance that is lower than planes that are targets of autofocus in industrial microscopes, biological microscopes detect less AF light than do industrial microscopes, and have a lower S/N ratio. This often leads to a situation where the detection of the focusing state is not conducted properly due to an influence of AF light reflected by the lens surface of the objective or of a lens of the optical system of the autofocus device (referred to as flare light hereinafter), imposing a limitation on the use of objectives that cause flare light.
In view of this problem, there is a countermeasure in which for example AR (Anti-Reflection) coating for suppressing the reflection of AF light, which is infrared (IR) light, is applied to the lens surface of an objective so as to suppress the generation of flare light.